Antimicrobial Resistance in the Intensive Care Unit: Mechanisms, Epidemiology, and Management of Specific Resistant Pathogens  Henry S. Fraimow, MD, Constantine Tsigrelis, MD  Critical Care Clinics  Volume 27, Issue 1, Pages 163-205 (January 2011) DOI: 10.1016/j.ccc.2010.11.002 Copyright © 2011 Elsevier Inc. Terms and Conditions

Fig. 1 Selection and transmission of antimicrobial resistance. (A) Selection of antibiotic resistant mutants after antibiotic exposure. (B) Superinfection with new antibiotic resistant bacteria after antibiotic exposure. (C) Horizontal transfer of resistance genes into a susceptible strain can occur through transfer of plasmids containing resistance transposons, by the direct transfer of resistance transposons from the chromosome, or by acquisition of free DNA. Critical Care Clinics 2011 27, 163-205DOI: (10.1016/j.ccc.2010.11.002) Copyright © 2011 Elsevier Inc. Terms and Conditions

Fig. 2 A cross-sectional view of a gram-negative bacterial cell. The cell envelope is composed of: (1) the outer membrane (OM), (2) a thin cell wall composed of peptidoglycan, (3) the periplasmic space, and (4) the cytoplasmic membrane (CM). The OM functions as a barrier that allows the diffusion of nutrients and other molecules into the GNB cell. The inner portion of the OM is composed of phospholipids, while the outer portion is composed of lipopolysaccharide (LPS). The OM also contains porin proteins, which allow for diffusion of hydrophilic antibiotics across the outer membrane. Most GNB have efflux pumps that traverse both the OM and CM and remove toxic substances that accumulate in the cell, but they also function to remove antimicrobials from the cell. The periplasmic space contains a variety of proteins including β-lactamases, which hydrolyze β-lactams. The CM is composed of a phospholipid bilayer with embedded proteins, and is involved in the transport of molecules into and out of the cytoplasm, including antimicrobials. The cytoplasm contains the genome, usually consisting of a single circular chromosome, and may contain one or more plasmids, all of which may carry genes that encode antimicrobial resistance elements. Ribosomes are also located in the cytoplasm. Critical Care Clinics 2011 27, 163-205DOI: (10.1016/j.ccc.2010.11.002) Copyright © 2011 Elsevier Inc. Terms and Conditions